[libvirt] [PATCH] support XEN_SYSCTL_INTERFACE_VERSION

xen-unstable c/s 20762 bumped XEN_SYSCTL_INTERFACE_VERSION to 7. I don't see how the interface change affects libvirt, other than failing xenHypervisorInit() since version 7 is not tried. The attached patch accommodates the upcoming Xen 4.0 release by checking for XEN_SYSCTL_INTERFACE_VERSION 7. If found, it sets XEN_DOMCTL_INTERFACE_VERSION to 6, which is also new to Xen 4.0. Regards, Jim